Question

hot water with surface area 2.5 m^2 & temperature of 92* C radiates heat into a room which is at 22* C

σ=5.67x10^-8 W/m^2 * K^4

what is the net heat transfer by radiation for 1.5 min, assuming the emissivity of boiling water is 1.0?

Answer 1

According to Stefan's law , energy emited per second, per unit area of a body

E=e(T4-T04)

Hence energy emited through the given area in given time

E'=e(T4-T04)At

Where e=emissivity of given body(boiling water=1

=Stefan's constant=5.67x10-8W/m2  K-4

T= temperature of hot water=92C=92+273=365K

T0=Temperature of surroundings=22C=22+273=295K

A=surface area=2.5m2

t=time=1.5minute=1.5x60=90sec

E'=e(T4-T04)At=1x5.67x10-8x[(365)4-(295)4]x2.5x90=1x5.67x10-8x[1.77x1010-.75x1010]x2.5x90=

E'=1x5.67x10-8x1.02x1010x2.5x90=1.3x105Joule